What is an Automatic Transfer Switch?

What is an Automatic Transfer Switch?

by | Nov 11, 2020 | Latest News & Articles

When you are browsing for a diesel backup generator, you will likely come across options for ATS / AMF or MTS panels. Most generators will also be noted as ‘ATS compatible’ within their description.

In this article, we are going to explain what is an ‘ATS or AMF’ panel when referred to on a diesel generator, like our Cummins powered genset range. We will also cover a basic outline of how they work. Hopefully, this will help you choose which one is best for your requirements.

You may also see references to MTS or 2 Wire Start on some generators. We have given the meanings below, but due to the complexity of these installations, a full article on MTS’ or 2 Wire systems will be written shortly. Follow our social media pages to keep up to date on Facebook or LinkedIn when we launch new articles.

What does ATS mean for a generator?

  • ATS – Automatic transfer switch
  • AMF – Automatic Mains Failure
  • MTS – Manual Transfer Switch
  • 2 Wire Start – A way of wiring a simple ‘on/off’ switch to your generator so you can start it up from a distance, or, in some instances this is required if you are using a generator in an installation with batteries and renewable energy sources.

Now, let’s look deeper into how the automatic transfer panels work.

How does an Auto Transfer Switch Work?

An ATS, or AMF are essentially the same thing. Both of these, an automatic transfer switch, or auto mains failure installation include panels, also known as switchgear which monitor the mains electricity coming into your property and will prevent downtime by turning your generator on and off, and switching your load (the house, property or equipment you are backing up) onto the generator and back to the mains when required.

An ATS panel will be installed after the meter outside your property (so that it does not count the electricity from the generator on your meter usage!), but before the consumer unit (previously known as a fuse board). You would need to install electrical cables from the generator, to the switchgear in the panel, but also another smaller cable, known as communication from the panel to an ATS or AMF port/terminal on the genset.

The ATS/AMF panel will monitor the main supply passing through it. Then, in the event of a power cut, or mains failure, the panel will send a signal to the diesel generator through the communication cable to turn it on. Once the generator has come up to the right speed, the panel will disconnect the load/property from being on ‘the grid’, and power it using the generator.

The panel continues to monitor the main cables, even though you are now being powered by the generator. Once the panel notices the grid is back up, it will work in reverse. It will connect your property or load back onto the mains supply, then send a signal to the generator to start it’s run down/cooling cycle and to stop.

Here is a simple image showing the basic positions of an ATS panel. Obviously these are not electrical schematics and in all instances, we advise you to consult a certified electrician or generator installation company for your install. 

Manual and Automatic Transwer switch panel diagrams when used with diesel generator

Why use an ATS?

Essentially, as the names imply, an Auto transfer switch, or auto mains failure system monitors for power outages, starts/stops the generator and switches you from mains to generator – and back again – without any interaction needed at all. This means it will work regardless of whether you are near your property and no intervention is required which is appealing.

The downsides of an ATS or AMF panel is that they can be more expensive to purchase, and to install, than a manual changeover switch and if the power outage is very short you may not want your generator starting up. You can set a relay, which basically delays the onset of the switch over and generator start up but this involves some work during the installation. 

What does ATS mean on generators?

When you notice generators being labelled as ATS or AMF compatible, or ATS ready – this usually means that they have a socket installed or a control panel which is ready for the communication cable to be wired up – the cable that ‘tells’ the generator to start or stop. In some instances, additional plugs or sockets may be required for the communication cable, but essentially, the genset itself is ready to work with an ATS/AMF/2 Wire start set up.

What size ATS do you need?

This varies depending upon the size of load or circuit you are looking to back up. The amount of power you need from your generator to power the appliances you want to run. As the power cables run through the ATS panel (for it to be able to switch between the mains power and the generator power it must break and remake the circuit), the ATS or AMF panel should have a slightly higher max rating than the max rating of your generator

We can give you some advice on the pros and cons of using an auto set up vs a manual set up, but consulting a professional company regarding the size of panel and set up is always advisable. If you consult an electrician on the size of generator that you require (usually defined by the max amperage draw you are using), they can also advise on the size of panel.

Generally, a residential property uses a 100 Amp mains breaker. This would mean, if you are using the full capacity of power available in your property you would be using around 23kW of power. Therefore you would need a generator that produces around 28kW to be running at it’s best, and an ATS panel that is 100Amp rated with a slight buffer for overload should you require it.

Automatic Transfer Switches – 3 Pole Vs 4 Pole…

When browsing for an ATS or AMF panel you will often see 3 Pole or 4 Pole noted.

This refers to the number of ‘cores’ in the cable you are using, or the number of connections/terminals within the panel.

3 Pole refers to a single phase, 230 volt set up. Just like on a household plug, you have 3 pins. One is the live, one is neutral and one is earth. So, if you have a 230 volt generator, to power your 230 volt property (which most residential are), you need a 3 Pole panel.

If you are using 400 volt equipment, and are backing up your load or property using a three phase generator, you would need a 4 pole panel.

You can read more about 230v and 400v and the differences in our blog here.

To summarise…

An ATS or AMF panel is a way to minimise the disruption of a power cut by automatically monitoring the grid and connecting you to the generator when needed, but they can add some additional cost to a project. However, as they are fully automatic they will work anytime of day or night, even if you are not at the property which does give you invaluable peace of mind.

All of our generators, including the Cummins powered generators we stock are ATS or AMF compatible, which also means they are MTS and 2 Wire start ready. This applies to our entire generator range, whether they are our Evopower EVO range which uses a ComAp control panel, or our Cummins powered UKC ECO range which uses Deep Sea Electronics control panels.

Protection from power cuts due to an ATS panel and Cummins Diesel Generator

About Genpower

Evopower generators are designed and distributed by Genpower Ltd, based in Pembrokeshire, Wales, UK.

Designing and building generators and power equipment since 2006 we have vast experience in the industry, which is shown in the high quality equipment in our ranges.

We are the sole distributor for Hyundai Power Products, P1 Power Equipment, Gardentek and we distribute Cummins powered gensets under our own brand Evopower.

With our large 120,000 sq. ft. distribution centre, offices and warehouse we hold a large amount of stock and have in-house technicians consistently working to improve our products, and expert sales, parts and aftersales departments available to answer any questions you may have, provide back-up and spare parts and – in the unlikely event something goes wrong, you can have piece of mind we are here to help. 

Genpower UK warehouse (resized)
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